Dominance of IMP-4-Producing Enterobacter cloacae among Carbapenemase-Producing Enterobacteriaceae in Australia

Abstract

ABSTRACTThe prevalence of carbapenemase-producingEnterobacteriaceae(CPE) has been increasing worldwide.blaIMPhas been reported to be the predominant carbapenemase-encoding gene withinEnterobacteriaceaein Australia. However, there are limited data currently available on CPE from Queensland, Australia. A total of 58 CPE isolates were isolated between July 2009 and March 2014 from Queensland hospitals. The clonality of isolates was determined by Diversilab repetitive sequence-based PCR. The isolates were investigated for the resistance mechanisms carbapenemase, extended-spectrum β-lactamase, and AmpC β-lactamase and for aminoglycoside resistance and plasmid-mediated quinolone resistance genes by PCR. The plasmid types associated with carbapenemase-encoding genes were characterized. The majority of the CPE wereEnterobacter cloacae(n= 29). The majority of Queensland CPE isolates were IMP producers and comprised 11 species (n= 48). Nine NDM-producingEnterobacteriaceaewere identified. One NDM-producingKlebsiella pneumoniaeisolate coproduced OXA-48. OneK. pneumoniaeisolate was an OXA-181 producer. The incidence of IMP producers increased significantly in 2013.blaIMP-4was found in all IMP-producing isolates.blaTEM,qnrB, andaacA4were common among IMP-4 producers. The HI2 (67%) and L/M (21%) replicons were associated withblaIMP-4. All HI2 plasmids were of sequence type 1 (ST1). All but one of the NDM producers possessedblaCTX-M-15. The 16S rRNA methylase genes found among NDM producers werearmA,rmtB,rmtC, andrmtF. The substantial increase in the prevalence of CPE in Queensland has been associated mainly with the emergenceE. cloacaestrains possessing HI2 plasmids carryingblaIMP-4over the past 2 years. The importation of NDM producers and/or OXA-48-like producers in patients also contributed to the increased emergence of CPE.